THE SHAPE AND WEIGHT OF EGGS IN RELATION TO THE 
SEX OF CHICKS IN THE DOMESTIC FOWL 1 
By M. A. Jull, Senior Poultry man , and J. P. Quinn, Poultryman, Bureau of 
Animal Industry , United States Department of Agriculture 
REVIEW OF PREVIOUS WORK 
A study of the causes that might 
affect the production of one sex or the 
other in the domestic fowl should 
have an important bearing on the 
practical aspects of the poultry indus¬ 
try and on current theoretical questions 
concerning sex determination. The 
senior author 2 has made a number of 
observations concerning the sex-ratio 
situation in the domestic fowl, includ¬ 
ing the following: 
1. There is no apparent correlation 
between egg weight and sex ratio. 
2. There is no apparent correlation 
between yolk weight and sex ratio. 
3. There is no apparent correlation 
between yolk water-content and sex 
ratio. 
The authors are not aware of any 
observations having been made con¬ 
cerning the relationship between the 
shape of the egg and the sex of the 
chick hatched from it. A solution of 
this problem is important in order 
that the result may be added to results 
already determined and also because 
of the prevailing opinion among many 
practical poultrymen that long eggs 
usually produce male chicks. The 
poultry office of the Animal Husbandry 
Division of the United States Depart¬ 
ment of Agriculture is continually 
receiving letters either stating that the 
longer eggs produce more males than 
the shorter ones or inquiring if such is 
not the case. The data presented in 
this study serve as an answer. 
The data in this study also deal 
with the relationship between the 
weight of the egg and the sex of the 
chick hatched from it. It has been 
stated above that the senior author 
found no correlation to exist between 
egg weight and sex ratio. This obser¬ 
vation was based upon the results 
obtained in determining the sex of 
chicks from eggs laid during the first 
year of production by 45 Barred 
Plymouth Rock pullets mated to 
Brown Leghorn males. The sex was 
determined of all embryos that died 
from the twelfth day to hatching time 
as well as of all chicks that hatched. 
There was found to be no correlation 
between weight of egg and sex of 
chick. 
On the other hand, in another study 
the senior author 3 found a significant 
difference between the weights of eggs 
from which males were obtained and 
those from which females were ob¬ 
tained. This was based upon data 
used in a determination of growth rates 
in the sexes of pure-bred Barred Plym¬ 
outh Rock chicks. The only egg 
weights taken into consideration were 
those producing the chicks on which 
growth rates were determined, the 
records for analysis being selected at 
the conclusion of the growth period. 
The weights of the eggs in which 
embryos died and the weights of the 
eggs producing chicks which died prior 
to the termination of the period of 
growth studied were not considered. 
From the sex standpoint there may 
have been a differential prenatal or a 
differential postnatal mortality, or 
both. The weights of the eggs pro¬ 
ducing the chicks which completed the 
growth test showed that the eggs 
which produced males were heavier 
than the eggs which produced females, 
52.11 ±0.41 and 50.05±0.53 gm. The 
difference in mean weights is 2.06 ± 0.67 
gm., a difference which is slightly more 
than three times its probable error and 
therefore barely significant. 
The case in which there was estab¬ 
lished no correlation between egg 
weight and chick sex was with eggs laid 
throughout the first year of production 
1 Received for publication June 23, 1924—issued January, 1925. 
2 Jull, M. A. the relation of antecedent egg production to the sex ratio in the domestic 
fowl. Jour. Agr. Research; XXVIII: 199-224, 1924. 
3 Jull, M. A. differential sex growth curves in barred Plymouth rock chicks. Sci. Arg. 
4: 58-65, illus. 1923. 
Journal of Agricultural Research, 
Washington, D. C. 
( 195 ) 
Vol. XXIX, No. 4 
Aug. 15, 1924 
Key No. A—76 
